Partizan, chasing a record fifth successive league title, have 42 points from 15 games after Eduardo Pacheco, Stefan Babovic and Zvonimir Vukic made light work of their visit to Metalac.
Second-placed Red Star lost ground with a 2-0 home defeat by Vojvodina Novi Sad behind closed doors, as the 1991 European Cup winners served a one-match crowd ban for violence during last month's city derby against Partizan.
The outcome piled more pressure on Red Star's Croatian coach, Robert Prosinecki, who conceded the perennial two-horse title race between Serbia's big two was all but over.
"It's hard to imagine we will be able to catch up with Partizan, and I am disappointed with today's lack of effort and passion," Proinsecki, who won the 1991 European Cup with Red Star as a player, told a news conference.
"None of the players could look me in the eye in the dressing room and say they did their best. You can have a bad day but there is no excuse for such a timid performance devoid of any hunger to win."
Second-half substitute Miroslav Stedvanovic was the architect of Vojvodina's win, scoring the first goal shortly after the hour and setting up the second for midfielder Marko Ljubinkovic in the dying minutes.
Brazilian striker Pacheco fired Partizan ahead with a superb first-time shot from 16 metres early in the game before Babovic curled in a delightful free-kick and Vukic completed the rout in the second half with a tap-in.
"We should have done better in Europe this term but overall I am pleased because it's been a while since someone was 10 points clear halfway through the title race," Partizan coach Aleksandar Stanojevic said.
"We have also developed two outstanding young players in Lazar Markovic and Marko Scepovic."
The league resumes on March 3, when Partizan are away to struggling top-flight newcomers Novi Pazar and Red Star are at home to sixth-placed Spartak Subotica.
